The present invention relates to paint spraying devices, and more particularly to automatic paint spraying equipment wherein a spray head is connected to the end of a movable robot arm, and the robot arm is controllable by means of a data processing computer or other programmable controller.
Paint spraying robots have been used in industry for a number of years, wherein a paint spray nozzle is attachable to the forward end of a robot arm, and the robot arm is controllable under automatic program control to direct the paint spray nozzle toward a workpiece. Improvements in such devices in recent years have enabled such robot-controlled spray nozzles to be manipulable to paint complex shapes, and to paint workpieces which move past the robot station on a conveyer line. For example, automobile and truck bodies have been painted by automated robot equipment, wherein such bodies are continuously moving along a conveyer line, and a robot station includes a sensor for detecting the presence of a particular shape body, and a robot control system enables the spraying of paint over the body contours even while the body continues its movement along the conveyer line.
Certain structures such as automobile and truck bodies do present difficult painting problems, however, even for automated robot equipment. For example, it is difficult for a robot to paint the inside surface of a body, which is usually totally enclosed except for door and window openings. Such painting necessitates the extension of the robot arm into the body while the conveyer is moving the body along, and the robot is required to quickly maneuver the spray nozzle to all possible painting positions inside the body while compensating for the movement of the conveyer line. In some cases this requires the robot to paint nearly directly backward towards itself, and present state-of-the-art in robot wrist and arm mechanisms have made it difficult to construct an arm having freedom of movement to cover all possible spraying directions.
Since the paint spray nozzle is generally fixed relative to the robot arm to which it is connected, limitations in the flexibility of the robot arm usually result in limitations with respect to the flexibility of freedom of movement of the spray nozzle. Further, since only a single spray nozzle is typically affixed to a robot arm, the amount of paint dispensed from the nozzle is usually predetermined and fixed by selection of the nozzle orifice opening. It has not been possible to apply paint through a spray nozzle to achieve a first paint thickness on one area of coating, and to achieve a second paint thickness on another area of coating, without making repeated passes at a particular area with a spray nozzle. In cases where the spraying operation is made on an article moving on a conveyer line, it is frequently not possible to make multiple passes over predetermined areas of the workpiece during the limited time in which the workpiece passes through the paint spray workstation. In such cases, multiple spray guns and additional spray booths have been necessary, to give the desired degree of paint thickness on areas of the workpiece where thickness variations are required. It is therefore desirable to provide a spray nozzle mechanism wherein automated robot control may be enhanced by the additional option of selecting spray nozzles for applying different amounts of paint to predetermined sections of the workpiece.